export default {
  PI: 3.14159265358979324,
  x_pi: 3.14159265358979324 * 3000.0 / 180.0,
  delta: function(lat, lon) {
    // Krasovsky 1940
    //
    // a = 6378245.0, 1/f = 298.3
    // b = a * (1 - f)
    // ee = (a^2 - b^2) / a^2;
    var a = 6378245.0;
    var ee = 0.00669342162296594323;
    var dLat = this.transformLat(lon - 105.0, lat - 35.0);
    var dLon = this.transformLon(lon - 105.0, lat - 35.0);
    var radLat = lat / 180.0 * this.PI;
    var magic = Math.sin(radLat);
    magic = 1 - ee * magic * magic;
    var sqrtMagic = Math.sqrt(magic);
    dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * this.PI);
    dLon = (dLon * 180.0) / (a / sqrtMagic * Math.cos(radLat) * this.PI);
    return { 'lat': dLat, 'lon': dLon };
  },
  // WGS-84 to GCJ-02
  gcj_encrypt: function(wgsLat, wgsLon) {
    if (this.outOfChina(wgsLat, wgsLon))
      return { 'lat': wgsLat, 'lon': wgsLon };

    var d = this.delta(wgsLat, wgsLon);
    return { 'lat': wgsLat + d.lat, 'lon': wgsLon + d.lon };
  },
  // GCJ-02 to WGS-84
  gcj_decrypt: function(gcjLat, gcjLon) {
    if (this.outOfChina(gcjLat, gcjLon))
      return { 'lat': gcjLat, 'lon': gcjLon };

    var d = this.delta(gcjLat, gcjLon);
    return { 'lat': gcjLat - d.lat, 'lon': gcjLon - d.lon };
  },
  // GCJ-02 to WGS-84 exactly
  gcj_decrypt_exact: function(gcjLat, gcjLon) {
    var initDelta = 0.01;
    var threshold = 0.000000001;
    var dLat = initDelta; var dLon = initDelta;
    var mLat = gcjLat - dLat; var mLon = gcjLon - dLon;
    var pLat = gcjLat + dLat; var pLon = gcjLon + dLon;
    var wgsLat; var wgsLon; var i = 0;
    while (1) {
      wgsLat = (mLat + pLat) / 2;
      wgsLon = (mLon + pLon) / 2;
      var tmp = this.gcj_encrypt(wgsLat, wgsLon)
      dLat = tmp.lat - gcjLat;
      dLon = tmp.lon - gcjLon;
      if ((Math.abs(dLat) < threshold) && (Math.abs(dLon) < threshold))
        break;

      if (dLat > 0) pLat = wgsLat; else mLat = wgsLat;
      if (dLon > 0) pLon = wgsLon; else mLon = wgsLon;

      if (++i > 10000) break;
    }
    return { 'lat': wgsLat, 'lon': wgsLon };
  },
  // GCJ-02 to BD-09
  bd_encrypt: function(gcjLat, gcjLon) {
    var x = gcjLon; var y = gcjLat;
    var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * this.x_pi);
    var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * this.x_pi);
    bdLon = z * Math.cos(theta) + 0.0065;
    bdLat = z * Math.sin(theta) + 0.006;
    return { 'lat': bdLat, 'lon': bdLon };
  },
  // BD-09 to GCJ-02
  bd_decrypt: function(bdLat, bdLon) {
    var x = bdLon - 0.0065; var y = bdLat - 0.006;
    var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * this.x_pi);
    var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * this.x_pi);
    var gcjLon = z * Math.cos(theta);
    var gcjLat = z * Math.sin(theta);
    return { 'lat': gcjLat, 'lon': gcjLon };
  },
  distance: function(latA, logA, latB, logB) {
    var earthR = 6371000;
    var x = Math.cos(latA * Math.PI / 180) * Math.cos(latB * Math.PI / 180) * Math.cos((logA - logB) * Math.PI / 180);
    var y = Math.sin(latA * Math.PI / 180) * Math.sin(latB * Math.PI / 180);
    var s = x + y;
    if (s > 1)
      s = 1;
    if (s < -1)
      s = -1;
    var alpha = Math.acos(s);
    var distance = alpha * earthR;
    return distance;
  },
  outOfChina: function(lat, lon) {
    if (lon < 72.004 || lon > 137.8347)
      return true;
    if (lat < 0.8293 || lat > 55.8271)
      return true;
    return false;
  },
  transformLat: function(x, y) {
    var ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x));
    ret += (20.0 * Math.sin(6.0 * x * this.PI) + 20.0 * Math.sin(2.0 * x * this.PI)) * 2.0 / 3.0;
    ret += (20.0 * Math.sin(y * this.PI) + 40.0 * Math.sin(y / 3.0 * this.PI)) * 2.0 / 3.0;
    ret += (160.0 * Math.sin(y / 12.0 * this.PI) + 320 * Math.sin(y * this.PI / 30.0)) * 2.0 / 3.0;
    return ret;
  },
  transformLon: function(x, y) {
    var ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x));
    ret += (20.0 * Math.sin(6.0 * x * this.PI) + 20.0 * Math.sin(2.0 * x * this.PI)) * 2.0 / 3.0;
    ret += (20.0 * Math.sin(x * this.PI) + 40.0 * Math.sin(x / 3.0 * this.PI)) * 2.0 / 3.0;
    ret += (150.0 * Math.sin(x / 12.0 * this.PI) + 300.0 * Math.sin(x / 30.0 * this.PI)) * 2.0 / 3.0;
    return ret;
  }
};